Negative-tone chemically amplified resists (NCAR) have been widely used in electron beam lithography for small dots or fine iso-lines. In general, NCAR, contains base resin, photo acid generator, curing agent, and additives such as a quencher. Referring now to FIG. 1, when NCAR 12 (on substrate 11) is exposed to an electron beam 13, a photo acid generator will release acid in exposed region 14, which will catalyze the cross-linking reaction of the base resin in the subsequent baking process. The degree of cross-linking will influence the dissolution rate of exposed NCAR allowing a resist pattern to be developed through the differential dissolution rates.
As the feature sizes approach 0.1 μm or smaller, reduction of line edge roughness (LER) becomes increasingly important. Many CD (critical dimension) reduction methods in the prior art do not have sufficient CD tolerance because LER has also increased substantially. In fact, LER can sometimes be greater than the total budget for CD tolerance. This is schematically illustrated in FIG. 2 where developed line 14 is seen to have rough edges 21. One can, in principle, always reduce the CD through extensive over-development since any incomplete or less cross-linked resists will be dissolved under aggressive development conditions. However, with such an approach, the LER also increases substantially. Additionally, the resist thickness also gets reduced.
Thus, the problem that the present invention addresses is how to precisely control line width in Ebeam resist patterns without an accompanying increase in line edge roughness and/or significant loss of thickness.
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 6,313,492, Hakey et, al. show an e-beam process with negative and positive resists. In U.S. Pat. No. 4,568,601, Araps et al. show an e-beam exposure and curing method for negative resists. Kumar et al. show an e-beam exposure process in U.S. Pat. No. 6,436,810 B1. US 2001-004765A1 (Miyagawa) shows a double exposure e-beam process while Minter et al. reveal a double exposure e-beam process to control liftoff in U.S. Pat. No. 6,218,090 B1.
The following publications of interest are also noted:    1. L. Pain, et al, Proc. SPIE, Vol. 3999 (2000) pp. 706-716    2. A. G. Timko, et al, J. Vac. Sci. Technol. B 19(6) November/December 2001, pp. 2713-2716    3. B. Wu et al. J. Vac. Sci. Technol. B 19(6) November/December 2001, pp.2508-2511    4. S. Yamamoto, et al, Technical bulletin from Sumitomo Chemical Co. Ltd., Osaka, Japan